1. Field of the Invention
The present invention relates to a platinum complex and an organic light-emitting device using the same and, more particularly, to a phosphorescent platinum complex and a phosphorescent organic light-emitting device using the same.
2. Description of Related Art
In general, the term “organic light-emitting phenomenon” refers to a phenomenon in which electric energy is converted to light energy by means of an organic material. The organic light-emitting device using the organic light-emitting phenomenon has a structure usually comprising an anode, a cathode and organic material layers interposed therebetween. Herein, the organic material layers may be mostly formed in a multilayer structure comprising layers of different materials, and contain an organic emissive layer that emits light by fluorescence or phosphorescence. An OLED generally comprises an anode, a hole source, an emissive layer (EML), an electron source and a cathode. The hole source may comprise a hole injection layer (HIL) and a hole transport layer (HTL). The electron source generally comprises an electron transport layer (ETL) and possibly an electron injection layer (EIL). Some OLEDs also comprise a thin layer of LiF between the electron source and the cathode. As shown in FIG. 1, there is shown a schematic representation of a typical OLED, comprising a substrate 100 and an anode 101, a hole transport layer 102, a hole injection layer 103, an emissive layer 104, an electron injection layer 105, an electron transport layer 106, a LiF thin layer 107 and a cathode 108 on the surface of the substrate 100 in sequence.
The emissive layer (EML), comprised of a host material doped with one or more luminescent materials, provides the function of light emission produced by excitons. The excitons are formed as a result of recombination of holes and electrons in the layer.
OLEDs are classified roughly into two types by a difference of mechanism of emission, namely the fluorescent OLED or phosphorescent OLED. It is well known that the phosphorescent OLED is advantageous from an aspect of emission quantum efficiency.
Owing to their potential to harness the energies of both the singlet and triplet excitons after charge recombination, transition metal based phosphorescent materials have recently received considerable attention in fabricating phosphorescent OLEDs. The main advantages are due to the heavy atom induced singlet-to-triplet intersystem crossing as well as the large enhancement of radiative decay rate from the resulting triplet manifolds. In this regard, numerous attempts have been made to exploit third-row transition metal complexes as dopant emitters for OLED fabrication, among which quite a few Pt(II), Os(II) and Ir(III) complexes have been reported to exhibit highly efficient device performances. Despite these developments, attempts to further expand the potential of the square planar Pt(II) complexes, in which the central metal ion possesses a higher atomic number than Os(II) and Ir(III) for efficient OLED applications, has encountered many intrinsic obstacles. For example, the PtOEP (H2OEP=octaethylporphyrin) type of emitter commonly has a ligand based phosphorescence with lifetimes as long as 30˜50 μs, so that saturation of emissive sites and a rapid drop in device efficiency at high drive current is observed. Also contributing to the poor device efficiency is the planar molecular configuration of many Pt(II) complexes, which leads to a stacking effect and hence the formation of aggregates or dimers that tend to form excimers in the electronically excited state.
In addition, as a light source for illumination or backlight, a white light is usually required. To realize a white OLED device, plural light emissive materials such as blue, green, red are used generally. However, blue phosphorescent materials have been the most difficult to prepare.